In general, this invention is directed to an electrochemical cell exhibiting improved current collection capability, and a method of making such an electrochemical cell. In one instance the electrochemical cell is a spirally wound cell, but the cell can be of any variety.
In a typical spirally wound electrochemical cell, a first conductive layer and a second conductive layer are separated by insulation. The conductive layers are offset from one another, so that the first conductive layer extends beyond the insulation and the second conductive layer in one direction. The second conductive layer extends beyond the insulation and the first conductive layer in an opposite direction. The layers are then rolled together to form a jelly-roll style electrode stack wherein the first conductive layer forms a positive electrode at one end of the stack, and the second conductive layer forms a negative electrode at a second end of the stack opposite the stack first end.
A first spiral space is defined in the first end of the jelly-roll by the portion of the first conductive sheet which is not layered with either insulation or the second conductive sheet. A second spiral space is defined in the second end of the jelly-roll by the portion of the second conductive sheet which is not layered with either insulation or the first conductive sheet. The positive and negative electrodes are then connected to terminals of a fluid tight casing for use as a battery. Before the casing is sealed shut, an electrolyte is put into the casing surrounding the electrodes. The electrolyte aids in the development of an electric potential difference between the electrodes in the cell.
In the typical electrochemical cell, the electrodes are connected to the terminals of the battery by connection portions extending from the electrode sheet itself, or by tap straps. Another method of connection is to edge weld the connection portions to the spiral end of the electrodes. These methods, however, suffer the problem of only being capable of carrying a limited amount of current from the cell. The tabs do not connect to a sufficient area of the electrode to carry larger currents associated with bigger batteries. Moreover, welding additional connection portions presents problems in manufacture of the batteries, such as limiting the area by which electrolyte can be introduced into the electrode, and increasing the cost as well as production time for the battery.